What California offers is ideas. Political movements and cultural trends start here and sweep across the country. Some ideas are born of genius, and they're priceless. But others come from hubris, and they're dangerous.

It's in the second category that you'll find California's Proposition 19, an initiative on the November 2 ballot that would make it legal for anyone who is 21 or older to buy small amounts of marijuana.

A recent survey by Public Policy Polling indicates that the majority of California voters support the proposition, called the Regulate, Control and Tax Cannabis Act of 2010, by 47 percent to 38 percent.

It's official. The country's most populous state is nibbling at poison.

Video: Parker: Legal pot a 'good stimulus'

It's official. The country's most populous state is nibbling at poison.
--Ruben Navarrette Jr.

One can see how this kind of measure would appeal to those who want to seem pragmatic, hip or enlightened --such as former Facebook executive Sean Parker, who is reportedly contributing $100,000 to the campaign for Proposition 19. The 30-year-old Parker -- a venture capitalist who founded the music-sharing system, Napster -- offered the donation after Facebook co-founder Dustin Moskovitz, contributed a total of $70,000.

A spokesman for the pro-legalization group Drug Policy Alliance boasted, "What's interesting here is that [Parker] is a member of the generation that really gets it."

What do supporters of Proposition 19 supposedly "get" that the rest of us are missing?

They insist that marijuana isn't as dangerous as other products that are legal, such as alcohol and tobacco. They point to the benefits of medicinal marijuana to alleviate pain and suffering for cancer patients. And, with a drug war raging south of the border, they say the most effective way to combat the Mexican drug cartels that bring their illicit cargo into the United State is to legalize the substance, undercut the profit and put the cartels out of business.

These are all perfectly fine arguments that are, to some of us, completely unconvincing.

If you decide that exposure to a given substance -- particularly the kind of consistent and sustained exposure that comes from a product being made readily available -- is harmful to individuals and the rest of society, then you will naturally put in place laws that make it illegal to possess the product.

That makes sense. So does this: If you legalize any kind of undesirable behavior -- from vagrancy to prostitution to identity theft -- you'll remove the stigma and get more of that behavior.

It's true that alcohol and tobacco are legal, but it's also true that we restrict the use of such products and levy high taxes on them to discourage people from abusing them. Why?

Because we recognize the harm these products cause and the damage they do. We're especially aware of this with alcohol, which, like marijuana, has the effect of relieving people of control over their faculties, impairing their judgment and dulling their sense of right and wrong. None of that is good for the rest of us.

The use of medical marijuana is a far cry from making the herb readily available to anyone who can purchase it.

In fact, medical marijuana dispensaries are concerned that they could be put out of business by competition with liquor stores selling the same product without the kind of regulation with which they must contend.

Under the current system -- established in 2003 by state law and in 1996 by a proposition -- you need a doctor's note to buy marijuana for medicinal use. The requirement could soon go out the window.

As for the drug war, I defer to the expert -- the person who has put his life and the lives of his family in danger to take the fight to drug traffickers: Mexican President Felipe Calderon.

He has strongly condemned Proposition 19, saying that it reflects lax attitudes toward drug consumption in the United States, which is the life's blood of the drug trade.

Calling the growing acceptance of marijuana use by the American public absurd, Calderon warns that should the measure be adopted. it would only drive up demand and undercut joint efforts by the United States and Mexico to combat the drug cartels. It's a subject he knows well.

"Drugs kill in production," Calderon said. "Drugs kill in distribution, as is the case in the violence in Mexico, and drugs kill in consumption."

In this case, we should listen to our neighbor. Recently, when a Mexican newspaper essentially handed over its coverage to the drug cartels, asking them what it could publish and what it couldn't, reasonable people in both countries condemned the decision to do so as a cowardly act of surrender.

But capitulation comes in many forms, and Proposition 19 is one of them. If you legalize drug use, you will get more drug use, with all the nasty side effects. It's that simple.

California is the birthplace of ideas, all right. But if voters make the mistake of approving this foolhardy measure, those who live in the other 49 states had better hope that this is one trend that stays on the left coast.

The opinions in this commentary are solely those of Ruben Navarrette Jr.